Polymer materials are frequently used for pipes for various purposes, such as fluid transport, i.e. transport of liquid or gas, e.g. water or natural gas, during which the fluid can be pressurized. Moreover, the transported fluid may have varying temperatures, usually within the temperature range of about 0° C. to about 70° C. Such pipes are preferably made of polyolefins, usually polyethylene or polypropylene.
Because of the high temperatures involved, hot water pipes of polymer materials represent a particularly problematic type of polymer pipe. Not only must a hot water polymer pipe fulfill the requirements necessary for other ordinary polymer pipes, such as cold water pipes, but in addition it must withstand the strain associated with higher temperatures. The temperatures of the hot water in a hot water pipe, typically used for plumbing and heating purposes, range from 30-70° C., which means that the pipe must be able to withstand a higher temperature than that for a secure long term use. Peak temperatures may be as high as 100° C.
According to the draft standard prEN 12202 a hot water polypropylene pipe must meet the requirement of at least 1000 hours before failure at 95° C. and 3.5 MPa pressure if it is a random copolymer.
Austrian patent AT 404 294 B discloses a pressure pipe which consists of a homopolymer of polypropylene which consists predominantly of the hexagonal β-form of polypropylene with a nucleating agent which is based on an amide. These pipes have an increased resistance to rapid crack propagation. The published Japanese patent application JP 05-170932 discloses polypropylene pipes for water supply purposes. It is disclosed, that by adding certain antioxidants to different kinds of polypropylene, the endurance time of these pipes can be increased. None of these documents discloses polypropylene pipes with an increased long-term pressure resistance.